Prestressed, split cylindrical electromechanical transducer

ABSTRACT

An electromechanical transducer is made from a member providing for the introduction of electrical energy and the conversion of such energy to mechanical vibrations radially. First means cooperate with the transducer member in limiting the vibrations of the member in a direction for radially contracting the member. When the transducer member has a narrow gap extending along the length of the transducer member, the first means includes a resilient member having a width greater than the width of the gap and disposed in the gap to prestress the transducer member and prevent the ends of the gap from contacting each other during such vibrations. Second means cooperate with the transducer member for limiting the vibrations of the member in a direction for radially expanding the member. The second means include at least one band extending circumferentially around the transducer member for limiting the mechanical vibrations of the member in a direction for expanding the member. Means are provided for introducing electrical signals to the transducer member to produce the mechanical vibrations.

This invention relates to electromechanical transducers for convertingelectrical energy to mechanical energy. More particularly, the inventionrelates to electromechanical transducers for safely producingsignificant amounts of mechanical power without damage to thetransducer.

Electromechanical transducers are advantageous because they provide aconversion between the electrical energy and mechanical energy. Forexample, when alternating current signals are introduced to anelectromechanical transducer, the transducer vibrates and producesmechanical or acoustical energy in accordance with such vibrations. Theconversion of electrical energy to mechanical energy has a number ofdifferent uses such as in loud speakers and in sonar applications.

Electromechanical transducers have been known for a considerable numberof years. In that period of time, substantial work has been performed toperfect the transducers. In spite of this, several basic problemsremain. For example, it has been difficult to convert large amounts ofenergy safehy from electrical energy to mechanical energy withoutdamaging the transducer. This has been particularly true at suchrelatively high frequencies as those between approximately fifteen (15)kilohertz and twenty (20) kilohertz. A considerable effort has been madeto resolve such difficulties but such efforts have not been entirelysuccessful.

As one example of the prior art, a transducer member has been wrappedwith wire and resin to cushion the vibrations of the member. Suchwrapping may have had some beneficial effect in cushioning thevibrations of the member but the wrapping also tended to dump thevibrations of the member and also absorb some of the energy producedfrom such fibrations.

This invention provides an electromechanical transducer which overcomesthe above difficulties. The transducer is able to operate safely withinparticular preset limits to deliver significantly greater amounts ofmechanical power than in the prior art. For example, the transducer isable to supply safely, without any fear of damage to the transducer, asmuch as five (5) to ten (10) times more power than in the prior art. Thetransducer is able to provide this power with optimal efficiency. Thetransducer is able to provide such mechanical power at relatively highfrequencies, such as between approximately fifteen (15) kilohertz andtwenty (20) kilohertz.

The transducer of this invention includes a transducer member which ispreferably disposed in the form of a hollow cylinder. The transducer isprovided with a gap which is provided with a thin width and which isdisposed along the axial length of the transducer member. Means areprovided for introducing electrical signals to the transducer member toproduce mechanical vibrations in the member.

First means cooperate with the transducer member for limiting thevibrations of the member in a direction for radially contracting themembers. The first means may include a resilient member having a widthgreater than the width of the gap and disposed in the gap to prestressthe transducer member and prevent the ends of the gap from contactingeach other during such vibrations.

Second means cooperate with the transducer member for limiting thevibrations of the member in a direction for radially expanding themember. The second means include at least one band extendingcircumferentially around the transducer member for limiting themechanical vibrations of the member in a direction for expanding themember.

The transducer of this invention has certain important advantages. Thefirst means limit the vibrations of the transducer member in a radiallycontracting direction and the second means limit the vibrations of themember in a radially expanding direction. In this way, considerableamounts of electrical energy can be introduced to the transducer memberwith the assurance that the mechanical power produced by the transducermember will not exceed the safe limits of the member. Furthermore, theimposition of the vibrations from a prestressed condition of thetransducer member increases the effiency of the operation of the member.

In the drawings:

FIG. 1 is an exploded perspective view of an electromechanicaltransducer constituting one embodiment of the invention;

FIG. 2 is a perspective view in assembled form of the electromechanicaltransducer shown in FIG. 1;

FIG. 3 is a sectional view of the transducer shown in FIGS. 1 and 2;

FIG. 4 is a perspective view of a modified electromechanical transducerof this invention; and

FIG. 5 is a sectional view of the modified transducer of FIG. 4.

In one embodiment of the invention, a transducer generally indicated at10 includes a transducer member 14 preferably having a hollowcylindrical configuration. The member 14 may be made from a suitablematerial such as a lead zirconate lead titanate ceramic or from anyother material well known in the prior art. As is well known in theprior art, the member 14 may be provided with a proper ratio of lengthto diameter to insure operation in a pure "hoop" mode. In other words,the member 14 may be constructed to vibrate in a radial direction.

The member 14 may be provided with a gap 16 extending axially along thelength of the member. The gap 16 may be formed by a diamond blade andmay be provided with a gap corresponding to the width of the blade. Thewidth of this gap may be a few thousandths of an inch.

The member 14 may then be forcibly expanded outwardly at the position ofthe gap 16 to open the gap by an additional small distance. Thisdistance may be a few thousandths of an inch. A resilient member 18 madefrom a suitable material such as a pure rubber or a silicone rubber isthen inserted in the gap 16 while the gap is maintained in its openedcondition. The resilient member 18 is provided with dimensions tomaintain the member 14 in a prestressed condition of a few thousandthsof an inch after the member has been released to close the gap 16.

At least one band 20 is then attached to the member 14 at the peripheryof the member. Preferably the band 20 is attached as by spot solderingto the member 14 in at least a pair of positions spaced around theperiphery of the member 14. The disposition of the band 20 is such thatit limits the radial expansion of the member 14. The band 20 may be madefrom a suitable material such as a braided wire. More than one band mayalso be used, particularly when the axial length of the transducer isrelatively great. Such bands may be spaced axially relative to oneanother along the length of the transducer.

A source 22 of alternating voltage may be provided. Connections may berespectively made from the source 22 to the inner and outer surfaces ofthe member 14. Upon the introduction of such signals to the member 14,vibrations are produced in the member in a radial direction.

The vibrations tending to contract the member 14 are limited by theresilient member 18. In this way, the ends of the member defining thegap 16 are not able to contact each other even when the member 14 issubjected to energy levels above its normal limits. This prevents themember 14 from being damaged by the introduction of such excessiveenergy.

In like manner, the band 20 limits the radial expansion of the member 14when the member if vibrated. This causes the radial expansion of themember 14 to be maintained within safe limits even when the member issubjected to energy levels above its normal limits.

Since the member cannot be stressed more than its pre-set limits, it canbe subjected to sufficient amounts of energy to insure that it willoperate at such prestressed limits. As a result, the transducer 10 canproduce amounts of power as high as five (5) to ten (10) times greaterthan the transducers of the prior art. For example, the transducer ofthis invention has produced five (5) to ten (10) times more power thanthe solid transducer disclosed in U.S. Pat. No. 4,038,348 issued to meon July 26, 1977.

The transducer of this invention has certain other important advantages.For example, the mechanical Q of the member tends to be increased in themember 14 relative to the mechanical Q of the member before it is cut toproduce the gap 16. This may result from the prestressing of the member14 in its rest position by the insertion of the resilient member 18 inthe gap 16.

The frequency of the mechanical vibrations of the member 14 also tendsto be increased in comparison to the frequency of the member without anygap in the member. For example, when the member vibrates at a frequencyof approximately fifteen (15) kilohertz without any gap, the provisionof the gap 16 and the insertion of the resilient member 18 in the gapcause the frequency of vibrations of the member 14 to increase toapproximately seventeen (17) kilohertz. This is contrary to what wouldhave been expected by a person skilled in the art.

Instead of disposing the bands 20 directly around the transducer member14, a cylinder 30 made from a suitable material such as steel may bedisposed around the member 14 as illustrated in FIG. 3. The cylinder 30may be provided with a gap 32 corresponding in dimensions to the gap 16and a resilient member 34 may be disposed in such gap. Bands 36 may thenbe attached to the cylinder 30 to limit the radial expansion of themember 14 and the cylinder 30. The cylinder 30 then serves as the memberproviding the mechanical power. Attachments may be made to this memberto provide the output power. The attachments may correspond to thosedisclosed in application Ser. No. 934,360 filed by me on Aug. 17, 1978.

Although this application has been disclosed and illustrated withreference to particular applications, the principles involved aresusceptible of numerous other applications which will be apparent topersons skilled in the art. The invention is, therefore, to be limitedonly as indicated by the scope of the appended claims.

I claim:
 1. An electromechanical transducer, including,a transducermember having a split configuration and made from a material providingfor the introduction of electrical energy and the conversion of thiselectrical energy to mechanical vibrations of the transducer member inthe radial direction, first means operatively coupled to the transducermember at the split in the member for prestressing the transducer memberto limit the vibrations of the transducer member in a direction forradially contracting the transducer member, second means operativelycoupled to the transducer member for limiting the vibrations of thetransducer member in a direction for radially expanding the transducermember; and third means for providing for the introduction of electricalsignals to the transducer member to obtain mechanical vibrations of themember in the radial direction.
 2. The transducer set forth in claim 1whereinthe transducer member is provided with a narrow gap extendingaxially along the length of the transducer member to define the split inthe member and the first means includes a resilient member normallyhaving a width greater than the width in the gap and disposed in the gapto prestress the transducer member and prevent the ends of the gap fromcontacting each other during the mechanical vibrations of the transducermember.
 3. The transducer set forth in claim 2 whereinthe gap has awidth of a few thousandths of an inch and the resilient member normallyhas a width a few thousands of an inch greater than the width of the gapto prestress the transducer member.
 4. The transducer set forth in claim1 whereinthe transducer member is in the form of a closed loopinterrupted by the split in the transducer member and the second meansincludes at least one band extending circumferentially around the loopedconfiguration of the transducer member for limiting the mechanicalvibrations of the transducer member in a direction for expanding thetransducer member.
 5. The transducer set forth in claim 4 whereinthetransducer member is provided with a narrow gap extending axially alongthe length of the transducer member to define the split in the memberand the first means includes a resilient member normally having a widthgreater than the width in the gap and disposed in the gap to prestressthe transducer member and prevent the ends of the gap from contactingeach other during mechanical vibrations of the transducer member.
 6. Thetransducer set forth in claim 4 whereinthe band is attached to thetransducer member in at least a pair of spaced positionscircumferentially around the looped configuration of the transducermember.
 7. The transducer set forth in claim 6 whereinthe transducermember is provided with external dimensions in the direction of thelooped configuration, and the electrical signals are introduced to thetransducer member, to produce mechanical vibrations of the transducermember in the radial direction.
 8. An electromechanical transducer,including,a cylindrical transducer member made from a material providingfor a change of electrical energy to mechanical energy and having a gapof thin circumferential dimensions along the axial length of thetransducer member, a resilient member disposed in the gap and normallyprovided with dimensions greater than those of the gap to prestress thetransducer member outwardly, at least one band extendingcircumferentially around the cylindrical configuration of the transducermember in tight relationship to the transducer member and attached tothe transducer member in at least one circumferential position to pressthe transducer member inwardly, and means for providing for theintroduction of electrical signals to the transducer member to obtainmechanical oscillations of the transducer member.
 9. The transducer setforth in claim 8 whereinthe band is attached to the transducer member tolimit the outward vibrations of the transducer member.
 10. Thetransducer set forth in claim 8 whereinthe resilient member is normallyprovided with a thickness slightly greater than the width of the gap toprestress the gap and the band is attached to the transducer member inat least a pair of positions spaced circumferentially around thetransducer member.
 11. In an electromechanical transducer,a transducermember having a split configuration to provide for a conversion betweenelectrical energy and mechanical vibrations of the member, and meansdisposed in the split in the transducer member for prestressing thetransducer member outwardly to limit the inward vibrations of thetransducer member.
 12. In the transducer set forth in claim 11,thetransducer member being provided with a narrow gap extending along thelength of the transducer member to define the split in the member andthe prestressing means including a resilient member normally having awidth greater than the width of the gap and disposed in the gap toprestress the transducer member and prevent the ends of the gap fromcontacting each other during the mechanical vibrations of the transducermember.
 13. In the transducer set forth in claim 12,the gap having awidth of a few thousandths of an inch and the resilient member normallyhaving a width a few thousandths of an inch greater than the width ofthe gap to prestress the transducer member.
 14. In the transducer memberset forth in claim 12,means for providing for the introduction ofelectrical energy to the member to vibrate the member.